The present invention relates to a gas sampling system, more particularly to a system for extracting small quantities of gas from a sealed package for sampling purposes.
In the packaging industry there is a need for ensuring that the quality of packaging materials is suitable for the safe storage of the packaged contents. In particular, in the food packaging industry it is important that packaging materials be selected from a group of available materials to best preserve the contents of the package over an extended shelf life. Virtually any packaging material has some degree of permeability to oxygen, and therefore virtually any packaging will eventually permit sufficient oxygen leakage into the package so as to contaminate or spoil the contents. However, there is a wide variation in the permeability of various packaging materials, and therefore it is possible to select materials which, while permeable, do have a sufficient non-permeability to oxygen so as to adequately serve as a food packaging material.
It is conventional practice in the packaging industry to back-flush packages with nitrogen (N.sub.2) before sealing the package. A further problem which is frequently encountered in this industry is the problem of poor sealing; a poor seal will permit oxygen leakage or permeation into the package, and can result in contamination or spoilage of the product contained within the package.
One of the periodic tests which are conducted in food processing plants, and in other plants where package permeability is of concern, is a test to measure the permeability of the packaging material. This test may be conducted by testing a sample of the packaging material in a device such as the Mocon "OXTRAN" test instrument, where an actual measure of permeability can be obtained. Although permeability testing of the packaging materials provides an excellent measure of the rate at which oxygen will permeate through the materials, such a test cannot be performed to test the package seal. The package seal is best tested by extracting a sample of gas from the interior of the package and then conducting a test on the gas sample to measure the oxygen concentration in the gas sample. One of the prior art techniques for extracting a sample of gas from the interior of a package is to utilize a needle and syringe. The needle is used to puncture the package and the syringe withdraws a sample of the interior package gas for subsequent sampling. The gas sample is injected into suitable test instrumentation in order to measure the oxygen concentration of the gas. The method is prone to error because it is quite likely that the sample gas may become mixed with extraneous oxygen concentrations in the atmosphere and elsewhere during the several steps required for the testing process. Another form of testing has been utilized, consisting of puncturing a package with a hollow needle and pumping a quantity of the packaging gas into a test station for purposes of measuring oxygen concentration. Care must be taken in using this technique and other techniques to avoid pressure inequalities in the system, as pressure variations can cause erroneous readings of oxygen content. The present invention is related to this form of testing device, to provide an efficient and reliable system for obtaining the necessary gas sample.